One of the most common toys enjoyed by children is building blocks. Basic building blocks are typically cube-shaped such that they are easily stackable. Often, the blocks include numbers, letters or pictorial representations on the sides.
Basic building blocks have further been modified for use in more complex puzzles and games. For example, U.S. Pat. No. 4,852,878 to Merrill discloses a game which utilizes eight detached playing blocks having different indicia sequences. The indices in each sequence have both a numerical character and a directional character. For example, in one embodiment, the indices are represented by the configuration of a drop, a heart, a crown, a clover, a star and a lightening bolt. The drop represents a numerical value of one and the apex in the drop determines the direction. The heart represents a numerical value of two in accordance with the two lobe portions and also has a direction based on its apex. The remaining indices are assigned numerical and directional values in accordance with the same pattern. Various games can thus be played by arranging the blocks according to the directional and/or numeric characteristics of the blocks.
U.S. Pat. No. 4,158,921 to Stolpen discloses the use of blocks for teaching relationships, similarities and differences in a number of subject matters. Each block includes at least two sets of indicia which bear a relationship to one another such that manipulation of the block discloses the relationship between the indicia or lack thereof.
While the aforementioned patents disclose blocks which are useful in learning relationships between individual elements, each side of the block bearing a representation of a single element, these patents do not disclose the use of blocks to teach relationships between subsets and members of subsets of a recognized set of living or non-living things.